Do not clear Client::m_mode_trash in handle_key, but in handle_available_input
Do not clear Client::m_mode_trash in handle_key, but in handle_available_input

handle_key can be called from exec_keys while running a hook, and a previous
key in exec_keys could have changed the mode. This would make the mode that
runned the hook deleted when the controls returns to it.

handle_available_input should always be called at top level, so can safely
clear the mode trash.

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